A wide variety of therapeutic techniques have been developed to correct or inhibit vascular diseases. Coronary artery disease (CAD), for example, is an adverse condition of the heart in which the blood flow to the heart muscle is partially or totally restricted by occlusive material in the coronary arteries which narrows the blood flow lumen. The occlusive materials deprive portions of the heart muscle of essential oxygenated blood.
CAD may be treated by a surgical technique referred to as coronary artery bypass graft (CABG) surgery. This surgical procedure involves supplementing blood flow to the heart muscle by grafting a non-native conduit such as a saphenous vein graft (SVG) to the heart. A first end of the SVG is connected to the ascending aorta (proximal to the occlusive material) and the other end is connected to the artery distal of the occlusive material. Although this technique has been useful for treating CAD in native coronary arteries, it is not uncommon for occlusive material to form over time in the SVG thereby necessitating additional therapy.
Percutaneous translumenal coronary angioplasty (PTCA) has gained wide acceptance as an effective and less invasive alternative to CABG surgery in certain patient groups. The PTCA procedure involves the use of an angioplasty balloon catheter, several types of which are well known in the art. The balloon catheter is inserted into the body via the femoral artery and navigated to the coronary arteries assisted by a guide catheter and (usually) a guide wire. The balloon is positioned across the restriction in the artery and subsequently inflated. The inflated balloon widens the restriction and restores blood flow to portions of the heart muscle previously deprived of oxygenated blood.
A PTCA balloon catheter typically has a manifold at its proximal end and a balloon at its distal end. The manifold facilitates connection to an inflation device which is used to inflate and deflate the balloon. An example of a conventional inflation device is disclosed in U.S. Pat. No. 5,019,041 to Robinson et al. which also includes a good discussion of related prior art inflation devices.
Prior art inflation devices are usually in the form of a modified 10 cc or 20 cc syringe. For example, the Classic.TM. inflation device (available from SCIMED Life Systems, Inc. located in Minnesota) includes a modified 20 cc syringe housed with an illuminated pressure gauge, threaded plunger and lock mechanism. This inflation device measures about 9.times.2.times.2 inches and weighs about 189 grams which renders it relatively bulky as compared to a conventional PTCA balloon catheter which measures about 0.039 inches diameter.times.57 inches length and weighs about 4 grams. Due to its size and weight, a typical inflation device may interfere with the physician's ability to delicately manipulate a balloon catheter through the vascular system. As a result, current day inflation devices incorporate a long flexible line as a part of the inflation device for connection to the catheter. Although the physician may choose to disconnect the inflation device from the balloon catheter while manipulating it, such additional steps are inconvenient, increase the time required for the procedure, increase the probability of introducing air into the system, and increase the probability that the vascular position of the balloon will be accidentally displaced when attempting to reconnect the inflation device. As such, it is desirable to minimize the size and weight of an inflation device to avoid these problems.
Due to their relatively large size, prior art catheter systems usually require two operators, namely one person to maintain catheter position and another person to operate the inflation device. Although the catheter position may be maintained by locking the guide catheter hemostatic seal (usually a Y-adapter) onto the catheter shaft, such a step is dependent on maintaining guide catheter position and is therefore not as reliable as maintaining position by manually gripping the catheter. Also, manually maintaining the catheter position allows the treating physician to easily make quick and accurate adjustments in balloon position between inflations.
An inflation device is preferably capable of inflating to pressures of at least 300 psi, and is preferably capable of drawing a near perfect vacuum (perfect vacuum=-14.7 psi at sea level). Prior art inflation devices commonly use a large bore (e.g. 20 cc) syringe to obtain a higher vacuum. In order to reach and maintain high inflation pressure, a relatively high force is required to actuate and hold a large bore inflation device. To overcome this problem, some prior art devices have utilized a threaded plunger and lock mechanism, an example of which is disclosed in Robinson '041. With a threaded plunger, a high longitudinal force and resulting high pressure may be generated by rotating the plunger with moderate actuation torque. The threaded plunger may be engaged by a lock mechanism to maintain the position of the plunger and thus maintain high pressures for a duration of time. Although such a feature reduces the necessary actuation force, it only adds to the size, weight and complexity of the inflation device and thus fails to overcome the corresponding disadvantages described previously.
Other prior art inflation devices utilize a small bore syringe (e.g. 1-2 cc) in combination with a large bore syringe (e.g. 10-20 cc) to generate high inflation pressures with relatively low actuation force. The small bore syringe takes advantage of the principal that force is equal to pressure multiplied by area (F=P.times.A) where the area of the small bore syringe is sufficiently small to reduce the force required to generate high pressure. Examples of such inflation devices are disclosed in U.S. Pat. Nos. 4,476,866 to Chin, 4,740,203 to Hoskins et. al., and 4,758,223 to Rydell. However, these inflation devices do not allow the small bore syringe to be used without the large bore syringe. As such, the combination of large and small bore syringes does not subtract but rather adds to the weight of the inflation device. Again, while these inflation devices reduce the actuation force required to generate high pressures, they do not overcome the problems associated with size and weight as identified previously.
In addition to the disadvantages associated with size and weight, prior art inflation devices have relatively high internal compliance. Compliance refers to the increase or decrease in volume of the fluid path (i.e. the inside of the inflation device and the inflation lumen of the catheter) in response to changes in pressure, in addition to the compressibility of the inflation fluid and any air trapped in the fluid path. High internal compliance is not desirable because it decreases the responsiveness of the system and increases the dampening effect on dynamic balloon response. High internal compliance also increases the tendency of the balloon to continue to expand after the lesion yields, thus increasing the probability of dissection. Furthermore, high internal compliance decreases balloon deflation rate which compromises the physicians ability to relieve ischemia and other adverse reactions to prolonged balloon inflation. Thus, it is desirable to reduce the internal compliance to overcome these disadvantages. Compliance may be reduced by providing a more rigid structure defining the fluid path and by decreasing the volume of inflation fluid and any air trapped in the fluid path. The volume of inflation fluid may be reduced by decreasing the volume of the fluid path, namely the inside of the inflation device and the inflation lumen of the balloon catheter.
In summary, there is a need for a catheter and inflation device system which minimizes size and weight, which is operable by a single person, which minimizes actuation force, and which minimizes internal compliance.